The ultimate goal of the proposed research is to describe basic substrates underlying the vestibular contributions to the maintenance of posture, muscle tone, reflexes, and execution of volitional movements. There are three basic goals in this proposal: An opportunity to develop expertise in quantitative immunocytochemistry. This training will be used initially in experiments to determine the proportion of vestibulospinal (VST) neurons that also stain with aspartate-like or glutamate-like immunocytochemistry. The proportion of VST neurons in which staining for these two excitatory amino acids are co-localized will also be determined. During the fourth year of award, these experiments will be extended to co-localization studies for the inhibitory amino acid transmitters GABA and glycine. In the future, these techniques can be used with other pathways, i.e. the commissural system and oculomotor pathways. This includes experiments for collateralization of vestibulospinal neurons as well as characterization of the distribution of immunohistochemically and anatomically-identified afferents on vestibulospinal neurons. An opportunity to learn basic and fundamental tools of Neuropharmacology. To learn receptor binding autoradiography, the distributions and interactions between agonists and antagonists of excitatory amino acids will be investigated. Basic neuropharmacology will be studied. Six months will be spent participating in electrophysiological experiments studying the role of excitatory amino acids in the vestibular nuclei. These studies will be initiated in the fourth year of the award. This award would provide the skills and the time necessary for the development of a productive research career. Future plans would continue in the direction of correlating anatomical subdivisions and vestibular pathways with neural transmitters, neural modulators, their agonists and antagonists. The long-term goal of this research will provide a comprehensive understanding of the anatomical and neurochemical organization of vestibulospinal pathways and the distribution of identified inputs of these pathways. The morphological and chemical substrates will be critical for eventual physiological analyses of sensory-motor interactions during normal vestibular ,stimulation, and, changes that occur, for example during behavioral compensation after destruction of the labyrinth.